XJ Torque Converter Swap For Mileage And Power

We embarked upon our ’98 Cherokee project during a time of astronomically high gas prices. Our goal initially was to build it to go off-road while not losing any on-road commuter-type mileage. We’ve stayed pretty close to the original plan, but over the last year or so we’ve been underwhelmed by the performance we were seeing.

The transmission was getting too hot. Downshifting only made things worse. Then we started getting codes that the torque converter wasn’t locking up. Now, we knew the torque converter was hurting. We’d been hearing that death rattle every time we took the Jeep wheeling, and with 245,000 miles on the original transmission and torque converter, it was no big surprise.

The first step (after disconnecting the battery, of course) is to support the transmission and T-case. If you have an aftermarket skidplate like we do, you won’t be able to disconnect any of the vital components until it is out of the way. However, the skid supports the transmission and T-case, so before removing it all willy-nilly, put something under the T-case output to support the drivetrain. If you are doing this at home, a jackstand on the T-case output is usually the best way to go.

But was a full transmission rebuild necessary, or was our torque converter the sole culprit as we suspected? We figured a torque converter swap could be done in a day. However, living 20 miles from the nearest parts store, and with no other Jeeps on hand if something went wrong in the driveway, we decided to enlist some expert help. We took the Jeep and the new torque converter down to Jeeps R Us in Laguna Hills, California. The crew had the install done in one morning, and we were back on the road before afternoon rush hour hit.

The results? Our suspicions were confirmed. Our gamble to change only the torque converter paid off this time around. We immediately noticed a seat-of-the-pants improvement in power, which the dyno verified. However, we were surprised to see that our power improvement didn’t translate into any increased mileage at the pump. So if your converter is chattery, your Jeep sluggish off the line, or your fluid temperature is inexplicably climbing, an inexpensive torque converter swap could buy many more miles for your automatic before a full rebuild is necessary.

Once you’ve got the skidplate out of the way, you are free to pull the driveshafts off the T-case. We are still running the stock driveshafts, so the front one unbolts from the T-case at the CV joint. The rear shaft unbolts from the differential and then just pulls out of the slip yoke on the T-case. Fasten the front shaft up with a bungee cord or zip ties, and be careful not to lose the U-joint caps off of the rear shaft when you lay it out of the way. Larry Garcia was the main wrench on our Jeep that day; he discovered that the rear pinion seal was leaking so he ordered and installed a new one. That would have been a long bike ride to the parts store for us.

The blue curves show the dyno run we did during our tire weight power shootout(baseline) and the orange curves show a similar run with the only change being the torque converter. You can see how we picked up almost 11hp and 14 lb-ft of torque at peak. More important than those peak numbers is the area between the before and after power curves. This is what our butt-dyno measures and is really noticeable in day-to-day driving.